add aria selected for canvas app center filters

fixes PLAT-556

test plan:

screen readers should be able to tell which filter is selected
you can tab through the apps now, and select one with space

Change-Id: Idf96f9418420dfe79ebe6d4451901cf2766589ab
Reviewed-on: https://gerrit.instructure.com/37767
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brad Humphrey <brad@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Nathan Mills <nathanm@instructure.com>